Back in September, Google Compute Engine added an autoscaling feature for select users; now Autoscaler is available to everyone through a new beta program. According to Google, "Autoscaler not only chooses the right number of instances but also adapts automatically based on how far the current state is from the desired target. This means Autoscaler performs well even in unexpected scenarios such as sudden traffic spikes."
Google Compute Engine is the company's IaaS; its PaaS, Google App Engine, already had an autoscaling feature. Amazon's cloud has had autoscaling since 2009.